Belgrave Road is at the heart of the Victorian street scene of Ventnor.
When, following a period of heavy sustained rainfall, the retaining walls supporting the road collapsed, a number of unique challenges had to be overcome in order to reinstate the section.
Not only does the site lie within Europe’s largest developed landslide complex, Ventnor, it is built into the rising landscape of this famous coastal town and therefore extremely confined.
The stabilisation project – one of the most complex undertaken on the Island – used local and national expertise to overcome challenging local geological and physical features to restore what is an important and unique piece of local infrastructure.
Island Roads’ initial priority was to ensure the safety of those in buildings and businesses above and below the failed 150-year-old wall with some temporary evacuations required because of the risk of further collapses and cascading debris.
In a first for the Island, specialist heavy-duty netting was installed across the failed slope as part of a risk-management plan developed to protect members of the public. Specialist roped access teams removed some of the debris by hand which was deemed a possible risk. All services were then diverted away from the failed wall section.
The next phase was survey and investigation work to inform the process of designing a solution.
The survey work, led by a project team of Island Roads and consultants Atkins, together with specialist contactors SOCOTEC and Corefix, was shortlisted for the award of Ground Investigation Project of the Year at the 2021 Ground Engineering Awards.
As part of the risk mitigation measures, 20 automated tiltmeters were installed across the site to monitor real-time movement across the potentially unstable site.
In developing the remedial and reconstruction plan, Island Roads and Atkins needed to overcome challenges including how to replace non- compliant historic masonry that formed the walls and parapets with alternative materials that satisfied the need of conservation officers. Furthermore, the site conditions severely restricted the size of plant that could be utilised to construct a remedial solution.
With piling not an option due to the size of plant required, a soil nail solution was adopted as this allowed installation with small scale plant and equipment. The facing was designed as a cut stone facing on reinforced concrete. The masonry parapet was specified to meet current containment standards for all highway users.
The top-down soil nail installation not only provided stabilisation of the slope in the temporary situation, but also formed part of the permanent works solution with the reinforced concrete wall construction, back fill, and masonry cladding being constructed in reverse from the bottom up once the site was made safe.
Construction was successfully completed to budget and programme in December 2022.
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